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Aquatic toxicity

Also known as
ecotoxicity, LC50, EC50

Aquatic toxicity is the harmful effect of a substance on aquatic organisms such as fish, invertebrates and algae. It is measured in standardized laboratory tests and reported as values such as LC50 and EC50, the concentrations that affect half of the test organisms.

What is aquatic toxicity?

Products used in cleaning, agriculture and industry often reach water, through wastewater or directly. Aquatic toxicity describes how harmful a substance is to the organisms living there. Because ecosystems are complex, toxicity is assessed in standardized tests on representative species from different levels of the food chain.

How it is measured

Common acute tests, published as OECD test guidelines, include:

  • Fish, typically over 96 hours, reported as an LC50: the concentration lethal to 50 percent of the fish.
  • Aquatic invertebrates, usually the water flea Daphnia, over 48 hours, reported as an EC50: the concentration that immobilizes 50 percent of them.
  • Algae, over about 72 hours, reported as an EC50 for growth inhibition.

Lower values mean a substance is more toxic. Chronic tests, run over longer periods, report concentrations with no observed effect.

How results are used

  • Hazard classification. Under the Globally Harmonized System of Classification and Labelling of Chemicals, substances with acute toxicity values of 1 mg/L or less fall into the most severe acute aquatic hazard category.
  • Ingredient standards. Programs such as EPA Safer Choice set aquatic toxicity criteria for ingredients, with stricter limits for direct release products.
  • Registrations. Chemical regulations such as REACH require aquatic toxicity data.

Toxicity is usually judged together with biodegradability: a toxic substance that breaks down quickly may pose less risk than a less toxic one that persists.

Frequently asked questions

The concentration of a substance in water that kills 50 percent of the test organisms, usually fish, within a set exposure period.

Many surfactants have some aquatic toxicity, because they act on cell membranes, and levels vary widely between types. Rapid biodegradation and wastewater treatment reduce the concentrations that reach the environment.

  • Biodegradability

    Biodegradability is the ability of a substance to be broken down by microorganisms into simpler substances such as carbon dioxide, water and biomass. For chemicals, it is measured by standardized tests that classify a substance as readily biodegradable, inherently biodegradable or persistent.

  • OECD 301

    OECD 301 is a set of six standardized laboratory tests, published by the Organisation for Economic Co-operation and Development, used to determine whether a chemical is readily biodegradable. A substance passes by reaching a set level of breakdown within 28 days.

  • EPA Safer Choice

    EPA Safer Choice is a U.S. Environmental Protection Agency program that certifies cleaning and other chemical-based products whose every ingredient meets EPA's safety criteria for human health and the environment. Certified products may carry the Safer Choice label.

Sources

  1. OECD Test Guidelines 201 (algae), 202 (Daphnia) and 203 (fish), Organisation for Economic Co-operation and Development
  2. Globally Harmonized System of Classification and Labelling of Chemicals (GHS), United Nations